1. Field of the Invention
This invention relates to a method for treating a liquid water-containing fluid stream being transported through a conduit in which at least a portion of the liquid water flashes to steam during transit. More particularly, the invention relates to such a method wherein the hot liquid water-containing fluid stream tends to build up a scale and/or corrode the surfaces of the conduit with which it comes in contact. By use of the method of this invention, the build up of scale is inhibited and/or any scale already formed is at least partially removed, and corrosion is mitigated.
2. Description of the Prior Art
Many industrial operations involve passing a hot water-containing fluid stream through a conduit under conditions, such as a lowering of the pressure, at which at least a portion of the hot water flashes to steam. If the hot water is a brine containing appreciable amounts of dissolved salts, this flashing is often accompanied by the formation of scale on the surfaces of the conduit contacted by the hot water-containing fluid stream. This deposition of scale tends to build up over a period of time and restrict further fluid flow through the conduit. This necessitates either operation at a reduced flow rate or an increase in the amount of power used to move the fluid through the conduit. In extreme cases, the conduit can become completely plugged with scale, and the industrial operation must be shut down for maintenance. An example of such an industrial operation involves the generation of steam which can be used as a source of heat or to generate power. Various methods of generating steam utilize fossil-fuel steam generators, nuclear steam supply systems and geothermal steam generator units.
Various proposals have been made to decrease the scale formation and/or corrosion in steam generating equipment. These methods include the addition to the feedwater of such materials as sodium phosphate to precipitate calcium ions and other hardness constituents present, sodium hydroxide to raise the pH of the system, a complex metal-chelating compound such as ethylenediamine tetracetic acid or nitrilotriacetic acid to complex the hardness constituents, and a neutralizing or filming compound such as ammonia, morpholine, cyclohexylamine, hydrazine, or octadecylamine acetate to produce an alkaline gas in the steam and react with the acidic gases produced from the feedwater.
The report "On-Line Tests of Organic Additives for the Inhibition of the Precipitation of Silica from Hypersaline Geothermal Brine II. Tests of Nitrogen-Containing Compounds, Silanes, and Additional Ethoxylated Compounds", J. E. Harrar, F. E. Locke, C. H. Otto, Jr., L. E. Lorensen and W. P. Frey, Lawrence Livermore Laboratory, Prepared for U.S. Department of Energy under contract No. W-7405-Eng-48, June 1, 1979 describes several classes of organic compounds which were screened as potential geothermal scale control agents. The leading antiscalant candidate was Ethoquad 18/25, methylpolyoxyethylene (15) octadecylammonium chloride. Similar quaternary ammonium compounds tested included dimethyl benzyl, coco, tallow and trimethyl ammonium chloride derivatives.
While each of the aforementioned treatments has met with some success in particular applications, the need exists for a further improved well treating process to reduce scale deposition and corrosion of metal equipment during the production and subsequent handling of well fluids containing hot brine, especially geothermal fluids.
Accordingly, it is a principal object of this invention to provide a method for inhibiting the deposition of scale onto and the corrosion of fluid handling equipment contacted by a hot water-containing fluid stream and for removing such scale from such surfaces.
It is a further object of this invention to provide such a method wherein the hot water-containing fluid stream is a steam generating fluid stream.
It is a still further object of this invention to provide such a method wherein the steam generating fluid is a geothermal fluid.
It is a still further object of this invention to provide such a method wherein the geothermal fluid comprises principally an aqueous brine.
It is another object of this invention to provide such a method wherein a treating material is admixed with the feedwater prior to the generation of the major proportion of the steam.
It is yet another object of this invention to provide such a method wherein the treating material is bled into a geothermal fluid at or near the producing interval of a well as the geothermal fluid is produced from a reservoir.
It is yet another object of this invention to provide such a method wherein the treating material is injected into the formation penetrated by a geothermal well.
Other objects, advantages and features of the invention will be apparent from the following description and appended claims.